The present invention relates to methods and apparatus for the examination and treatment of internal organs of the human body.
It is already known to make an internal examination of an internal human organ, without recourse to surgery, by means of equipment which makes use of the transmission and receipt of ultrasonic signals.
International application nos. WO89/04142 and WO90/14601 disclose two such systems.
In these systems a catheter is provided at its distal end with a piezo-electric crystal transducer array made up of a plurality of transducer segments arranged in an annular or cylindrical configuration around the end of the catheter or an extension of it.
In these disclosed systems the array typically consists of twelve transducer elements although it can be a larger number, e.g thirty-two or sixty-four. The method of energising the transducer array disclosed in these applications consists of (in the case of the twelve element array) energising four transducers at a time, each of the four transducers being distributed 90.degree. apart around the periphery of the annulus or cylinder. There are thus three sets of four transducer elements each arranged in a cruciform configuration so that as each cruciform is successively energised there is provided, as it were, a rotating cruciform ultrasonic beam.
The present invention is concerned with providing an improved energisation arrangement for generating so-called two-dimensional B-mode images in real time. Our earlier application WO90/14601 was also concerned with the provision of such images.
Ultrasound beam-forming from a transducer array of the kind referred to above relies on the received echo signals generated by the discrete transducer elements making up the array being delayed by differing amounts in order to get the individual echo signals into phase with another and then summing the echo signals in order to provide the signal from which an image can then be produced. The delays that are required will depend upon the varying distances of the individual transducers from the reflecting surface and will be selected to electronically focus the reflected echo signals.
In known ultrasonic systems having an array of transducers it is common to have several transducers energised at once and for the resultant echo signals to be handled by a plurality of parallel processing channels. The advantage of this arrangement is that the processing can be done in real time using analog hardware.
FIG. 1A illustrates the essence of this kind of prior art arrangement in which a plurality of discrete transducer elements 1 (typically 1a, 1b, 1c, 1d, and 1e) are individually connected to a summing circuit 2 through associated individual delay lines 3, these delay lines introducing delays which ensure that all the signals from a designated point (focus) are in phase on arrival at the summing circuit 2. The element group is scanned along line 1 which equals the result of signals from 1a, 1b, 1c, 1d and 1e, and defines a scan line 1. Another group 1b, 1c, 1d, 1e and 1f would then define an adjacent scan line 2.
Stepping through element groups in this way will define a raster of scan lines to give a 2-D image.
FIG. 1B illustrates the position where analog delay lines are used. In this arrangement the signals are not sampled and the signals remain in an analog and unsampled form until after the generation of scan lines.
FIG. 1C illustrates the position if one wishes to take advantage of digital processing. In this arrangement digital delay lines are used and the data is sampled. The sampling intervals must be the minimum delay increment (or accuracy). In practice this means that the sampling frequency needs to be at least 20 times the ultrasonic frequency. If this arrangement were used in connection with the field of the present invention this would means having a sampling frequency of 400 MHz. This in turn would put great demands on the hardware that would be necessary and is the approach which is adopted in U.S. Pat. No. 4,917,097 (Endosonics) where there is sampling at 400 MHz. In this prior art arrangement the delays are then achieved by simple clock delays.
The present invention is concerned with providing an arrangement which will overcome the disadvantages of the kind of system disclosed in U.S. Pat. No. 4,917,097.